Streaming a single media track to multiple clients

ABSTRACT

A system and method are provided for streaming a media track to multiple clients using a single copy of the track&#39;s metadata, rather than making separate copies of the metadata for each stream. A media track&#39;s metadata includes information that is used to identify and locate media corresponding to different time positions in the track or media program. Sharing one copy of the metadata among multiple client streams promotes more efficient use of a media streaming server&#39;s resources. When a media track is first requested, a track object is generated to store and allow access to the metadata. For each client stream, a separate track handle object is created to manage access to the metadata for the stream&#39;s specific context. The streamed media track may be part of a live media event or may be part of a pre-recorded media program.

This application claims the benefit of Provisonal Application No.60/195,755, filed Apr. 8, 2000.

BACKGROUND

This invention relates to the field of computer systems. Moreparticularly, in a media streaming system in which a track of media hasassociated metadata that provides timing, offset and other information,an apparatus and methods are provided for streaming a media track tomultiple clients with just one copy of the track metadata.

Media streaming systems are designed to stream media programs andevents, which may be pre-recorded or live, to client devices (e.g.,computers, media players). A client can play a media stream as it isreceived (i.e., before the stream is complete), thereby allowing fast,or even real-time, enjoyment of the media program or event.

Streamed media is often composed of multiple tracks. For example, anaudiovisual program generally includes at least one audio track and atleast one video track. Each track includes media of the appropriate type(e.g., audio, video), and may also include metadata that is used tostream the media correctly. A track's metadata may include informationfor identifying a media segment or sample (or other unit of media) thatshould be played for a given time index within the program, fordetermining where that segment or sample is located in the file, etc. Amedia track's metadata may thus be used by a media streaming server tostream the media track in the correct sequence, with appropriate timing,and so on.

When streaming a media track or program to multiple clients, existingsystems usually store separate copies of each track's metadata for eachclient. More specifically, from a media file containing the media to bestreamed, these systems repeatedly extract and store the metadata eachtime a new client requests the media. When serving a large number ofclients, this could require a significant amount of the server'sresources (e.g., memory, processor, disk usage), and may limit thenumber of clients the server can support.

Also, some existing systems typically allocate just one file descriptor,to be shared among all clients receiving a particular media stream, foraccessing the media file containing the media being streamed. This canlead to a great deal of contention among the client streams as each oneattempts to seek to (i.e., find) and extract a different media segmentor sample.

Yet further, when streaming a multi-track media program to a client,existing media streaming systems attempt to maintain synchronizationbetween the tracks so that the appropriate corresponding track media isstreamed or played for each time unit of the program, but may beincapable of regaining synchronization if it is lost. For example, ifthe media for one track is received (e.g., from a storage device) at aslower rate than the media for another track, an existing mediastreaming system may simply continue streaming the media, even if thetracks get further and further out of synchronization. Other systems maysimply halt a media stream if synchronization is lost, withoutattempting to correct the situation.

SUMMARY

Therefore, in one embodiment of the invention, an apparatus and methodsare provided for sharing one copy of a media track's metadata forstreaming the media track to multiple clients.

In this embodiment, one file track is generated to store the metadata ofa single media track. For a media program comprising multiple tracks, aseparate file track is generated for each track. For each client streamof the media, separate file track handles are established. Each filetrack handle acts as an interface between its client stream—differentclient streams may be at different time indices within the media—and thesingle instance of media metadata.

In another embodiment of the invention, a single file descriptor isshared among all file track handles associated with a single mediatrack, for accessing the file storing the track's media.

DESCRIPTION OF THE FIGURES

FIG. 1 is a block diagram depicting a server configured to stream mediain accordance with an embodiment of the present invention.

FIG. 2 is a block diagram depicting the use of a single copy of mediatrack metadata to stream the media to multiple clients, in accordancewith an embodiment of the invention.

FIG. 3 depicts one configuration of program objects cooperating tostream a media track to multiple clients with a single copy of thetrack's metadata, in accordance with an embodiment of the presentinvention.

FIG. 4 comprises a flowchart demonstrating one method of streaming amedia track to multiple clients with a single copy of the track'smetadata in accordance with an embodiment of the present invention.

FIG. 5 depicts one configuration of program objects for resynchronizingmedia within a media stream, in accordance with an embodiment of thepresent invention.

FIG. 6 is a flowchart demonstrating one method of resynchronizing mediawithin a media stream in accordance with an embodiment of the presentinvention.

DETAILED DESCRIPTION

The following description is presented to enable any person skilled inthe art to make and use the invention, and is provided in the context ofparticular applications of the invention and their requirements. Variousmodifications to the disclosed embodiments will be readily apparent tothose skilled in the art and the general principles defined herein maybe applied to other embodiments and applications without departing fromthe spirit and scope of the present invention. Thus, the presentinvention is not intended to be limited to the embodiments shown, but isto be accorded the widest scope consistent with the principles andfeatures disclosed herein.

The program environment in which a present embodiment of the inventionis executed illustratively incorporates a general-purpose computer or aspecial purpose device such as a computer server configured to providedata or media streaming services to computers or communications devicesof virtually any configuration (e.g., wired, wireless, portable,desktop). Details of such computers and other devices (e.g., processor,memory, data storage, display) are well known and may be omitted for thesake of clarity. Further, embodiments of the invention are described asthey may be implemented in an object-oriented programming environment.Suitable variations of embodiments may be implemented using otherprogramming models or frameworks, as will be appreciated by one skilledin the art.

It should also be understood that the techniques of the presentinvention might be implemented using a variety of technologies. Forexample, the methods described herein may be implemented in softwareexecuting on a computer system, or implemented in hardware utilizingeither a combination of microprocessors or other specially designedapplication specific integrated circuits, programmable logic devices, orvarious combinations thereof. In particular, the methods describedherein may be implemented by a series of computer-executableinstructions residing on a storage medium such as a carrier wave, diskdrive, or computer-readable medium. Exemplary forms of carrier waves maytake the form of electrical, electromagnetic or optical signalsconveying digital data streams along a local network or a publiclyaccessible network such as the Internet.

In one embodiment of the invention a media or data streaming server isconfigured to stream media or data to multiple clients. A media programor event that is to be streamed to multiple clients includes one or moretracks (e.g., audio, video), each of which may be stored in one or moremedia files. When a first request for the media program is received, thetrack's metadata is retrieved and stored in a file track. The metadatamay include information regarding: timing (e.g., to synchronize thetrack's media with other program tracks), locations of media segments orsamples (or other units of media) within a media file, hierarchies ofmedia units (e.g., chunks, samples that comprise a chunk), edit tables,etc.

For each client to which the media track is to be streamed, separatefile track handles are established to reference metadata within the filetrack. Thus, instead of storing separate copies of the track metadatafor each client stream, each client's file track handle references(e.g., with pointers) the single file track to retrieve timing location,locate media segments in a media file, etc. Further, each file trackhandle is allocated a file descriptor into the track's media files, forseeking and retrieving media.

Specific embodiments of the invention are described below as they may beimplemented for streaming QuickTime media from a UNIX-based computersystem, such as a system executing the Solaris™ operating system by SunMicrosystems, Inc. Such embodiments may be modified for use with othertypes of media and other computer systems, as may be understood from thefollowing descriptions.

An Illustrative Media Streaming Server

Media streaming allows a user to receive and enjoy media content withouthaving to wait until the full program or presentation is downloaded tohis or her client device. For example, the user can enjoy a pre-recordedprogram, or experience a live event in real-time, without waiting untilthe full program is received.

Media may be streamed in unicast or multicast mode. In unicast mode thestreaming server maintains a dedicated connection to each receivingclient device, which grants a user great control over his or her stream.He or she may, for example, be able to pause a stream, rewind orfast-forward through the streamed media, or perform other controlfunctions. However, this can lead to inefficient use of bandwidth for alarge number of users. In multicast mode, the media streaming serverstreams a program to multiple users simultaneously, thereby using lessbandwidth. This type of streaming is thus comparable to a traditionalbroadcast, and users have little control over their individual streams.Live events may normally be streamed in multicast mode, because it ismore efficient for serving large numbers of users. And, because it is alive event being enjoyed in real-time, there is little need tomanipulate the streamed media.

A media streaming server according to a present embodiment of theinvention may operate in a “reflection” mode of operation, in which theserver receives a media stream from another streaming system or server(usually in multicast mode), and forwards the media to one or more users(in unicast or multicast mode).

Streaming real-time media places constraints upon the issuing server,because delivery of each frame or other unit of the media must beperformed in a specified order and within a certain period of time.Thus, despite the number of clients it serves, a media streaming servermust strive to meet the demands of streaming real-time media so that thequality of service to the users does not drop to an unacceptable level.For example, regardless of the type of program (i.e., live orpre-recorded) and mode of streaming (i.e., unicast or multicast),streamed media is generally compressed to decrease the bandwidth that itconsumes in transit, thus helping to ensure timely delivery of media toa client.

A media streaming server according to one embodiment of the invention isconfigured to stream QuickTime media and/or other forms of media, in aunicast or multicast mode, over a proprietary or publicly accessiblenetwork such as the Internet. Media streams are formatted according to aset of protocols compatible with the transmission medium. In particular,when streaming QuickTime media the server may be configured for RTSP(Real-Time Streaming Protocol) to facilitate a client's control of amedia stream, RTP (Real-Time Transport Protocol) to deliver the streamto the client and/or receive media from another source, RTCP (Real-TimeTransport Control Protocol) to receive or exchange information regardingthe quality of a stream, SDP (Session Description Protocol) to describemedia to the client, etc. Other embodiments may be configured for othermedia protocols.

FIG. 1 depicts media streaming server 102, configured to streamQuickTime media according to an embodiment of the invention. In FIG. 1,media streaming server 102 serves clients 110, 112. The media that isstreamed to the clients may comprise a pre-recorded program retrievedfrom storage device 104 or a real-time program received from server 130(e.g., as part of multicast broadcast 130 a). Media streaming server 102may thus stream live events (e.g., concerts, news broadcasts, sportingevents), movies, documentaries, training videos, educational programs orclasses, etc.

Media streaming may require multiple connections between media streamingserver 102 and a client. In the embodiment illustrated in FIG. 1, afirst connection is made for RTSP (e.g., connection 110 a, connection112 a) to allow a client to control a media stream. In particular, aclient uses an RTSP connection to send commands to the media streamingserver. The media stream commands that a client may submit to the serverin this embodiment include commands such as Options, to receive a listof supported commands; Describe, to prompt the server to describe amedia program; Setup, to identify desired tracks it would like toreceive (wherein each track may be a different media form, such asvideo, audio, etc.); Play, to play a media track or program; Pause, totemporarily stop streaming; Teardown, to end a stream; etc. Thus, client110 may, for example, establish RTSP connection 110 a with server 102and issue the Describe command to receive a description of the contentand tracks available for streaming. Client 110 may then submit a Setuprequest for one or more tracks.

When a client issues a Setup command to the server, the serverestablishes an RTP connection (e.g., connection 110 b, connection 112 b)and an RTCP connection (e.g., connection 110 c, connection 112 c) forthe selected track(s). When the Play command is received, the serverstarts streaming media packets to the client through the RTP connection.And, the server and client may exchange RTCP packets, through the RTCPconnection, that describe the quality of the stream. When a Teardowncommand is issued, the server closes its related stream connections withthe issuing client.

The various connections employed by the media streaming server mayutilize TCP (Transport Control Protocol) sockets for a compatiblecommunication medium through which the server and a client communicate(e.g., the Internet). In other embodiments of the invention, the socketsmay be configured according to a different protocol (e.g.,HTTP—HyperText Transport Protocol, FTP—File Transfer Protocol).

As already described, media streaming server 102 of FIG. 1 may streamreal-time or live media to clients and may also stream pre-recordedmedia. Further, in the reflection mode of operation, the media streamingserver may redirect to clients media that it receives from anotherentity, such as a live event, a video camera, a broadcast from anotherserver (e.g., server 130), etc. In this situation media streaming server102 acts as a client and receives media packets via an RTP connectionestablished with the entity.

Clients 110, 112 are equipped with suitable media players for playingthe media streamed from media streaming server 102. For QuickTime mediastreaming, the clients may operate a QuickTime player such as thatavailable from Apple Computer, Inc. Client computing devices may operatevirtually any operating system for which a suitable media player isavailable (e.g., Solaris, Mac OS, Windows, Linux). Because clientdevices may have relatively low-bandwidth communication capability(e.g., 56K modem), media streams may be sent with relatively lowbit-rates. Higher bit-rates may, of course, be implemented for morerobust clients. Clients may identify media to be streamed to them bysubmitting a URL (Uniform Resource Locator), file name, program name(e.g., name of a movie, song title), etc.

U.S. patent application Ser. No. 09/828,052, filed on Apr. 6, 2001 andentitled “Method and Apparatus for Handling Events Received at a ServerSocket,” discloses a configuration of media streaming server 102 forstreaming media to multiple clients through a limited number ofcommunication sockets, and is hereby incorporated by reference.

Streaming Media to Multiple Clients With a Single File Track

In one embodiment of the invention, a media streaming server streamsmedia that is accompanied by metadata to facilitate the streamingprocess. For example, metadata for a QuickTime media track may indicatewhich unit or piece of media (e.g., audio sample, movie segment)corresponds to a given time index within the media's program, and whereto find it within a media file. In this embodiment, the metadata may beassembled (e.g., extracted from one or more media files for a givenmedia track) just once, but may be used to facilitate streaming of thattrack to multiple clients. This scheme is thus more efficient thanexisting streaming systems in which separate copies of the metadata areassembled for each individual client stream.

The media data, once extracted with the help of the metadata, is placedinto RTP packets and streamed to the clients. The media data may beprepared for streaming in virtually any format that can be handled by aclient. In particular, the media may be placed into packets withoutaltering its coding, compression or other attributes.

Illustratively, a client may request a media stream comprising multipletracks, or may individually request specific tracks. Each track has itsown metadata and may be sent to a client as a separate stream (i.e.,multiple tracks may or may not be combined into a single stream). Asdescribed above, in one embodiment of the invention the media is sent inRTP packets, in which case the streaming may be controlled by a clientvia RTSP commands and the quality of a stream may be reported via RTCP.In other embodiments of the invention, other suitable protocols areemployed.

When the media streaming server is operating in a reflection mode, inwhich it receives media (as RTP packets) from a source and streams themto clients, metadata for the media may be received with or in advance ofthe media.

FIG. 2 depicts the use of a singleton file track and multiple file trackhandles to stream a media track to multiple clients without separatelyextracting or making separate copies of the track's metadata, accordingto one embodiment of the invention.

In the illustrated embodiment, media program 200 includes audio track202 and video track 204. Each track includes its indicated type of mediafor the program (i.e., audio, video) and metadata that, among otherthings: identifies which media unit (e.g., audio sample, video frame)corresponds to a given time index in the media program; identifies whichchunk (e.g., collection of media units) a given unit belongs to or isincluded in; lists the media units within a given chunk; identifieswhere a given chunk or media unit is stored within media program file200; includes edit tables that allow content tools to insert or deleteparts of tracks without copying or compacting the entire track (e.g.,they allow a track to be fragmented); etc. Illustratively, audio track202 and video track 204 are stored as separate files (or sets of files).Alternatively, however, different types of tracks or portions ofdifferent types of tracks may be stored in a single file.

A media track's metadata may be stored contiguously within the file(s)containing the track's media, may be distributed throughout the track'smedia file(s), or may even be stored as a separate track.

In accordance with this embodiment of the invention, each track'smetadata is extracted and stored in separate file tracks. Thus, themetadata for audio track 202 is assembled as file track 212, while themetadata for video track 204 is stored in file track 214. The differenttypes of metadata within a track may be stored as separate tables,lists, or other data structures.

For each client that a track of the media program is being streamed to,separate file track handles are established. Thus, for client 230 a,file track handles 222 a, 224 a are established for accessing themetadata of file track 212 and 214, respectively. Similarly, for client230 b the metadata stored in file track 212 for audio track 202 isaccessed by file track handle 222 b, while the metadata of file track214 for video track 204 is accessed by file track handle 224 b.Illustratively, each file track handle includes one or more pointers orother references into the associated file track, with which to accessthe various types of information.

In addition, each file track handle, or set of file track handles for agiven client stream, may be allocated a separate file descriptor foraccessing the media file(s) that store a track's media. Thus, in theembodiment of FIG. 2, in which audio track 202 and video track 204 arestored in separate files, each of file track handles 222 a, 222 b, 224a, 224 b is allocated its own file descriptor for locating andextracting media for streaming.

While streaming media to a client (e.g., after the client requests atrack or program be played), the file track handles for the client'sstream access the file tracks to determine the proper sequence of media(i.e., the media unit(s) to stream for each time index of the media).With this information, the file track handles extract the media from themedia file(s) so that it can be placed into RTP packets (or packetsconfigured according to another suitable protocol) and streamed to theclient via an RTP connection. When a client terminates its stream, thefile track handles are deleted.

In one embodiment of the invention, a file track is configured tomonitor the number of file track handles maintaining references to it.In this embodiment, when all client streams of the related media trackhave been terminated, the file track may remove itself and thereby freeadditional resources for other processes or media tracks.

FIG. 3 depicts several program objects employed in one embodiment of theinvention. Appropriate corresponding program modules configured tooperate similarly to the illustrated program objects may be generatedfor computer systems with non-object oriented methods of programming.

In this embodiment, Track 302 represents a class of objects configuredto assemble metadata for a media track and allow multiple file trackhandles to use the metadata on behalf of different client streams.Multiple types of Track objects may be generated from Track 302, such asLiveTrack 320 for assembling metadata for streaming live or real-timeevent media, and FileTrack 322 for assembling metadata for stored orpre-recorded media. In one alternative embodiment of the invention, onetype of track object (e.g., FileTrack 322) may be configured tofacilitate streaming of both pre-recorded and live media. In yet anotheralternative embodiment, live media may not be in the form of tracks andmay therefore be served to clients in some other manner.

QuickTime FileTrack 322 a and MPEG FileTrack 322 b represent FileTrackobjects configured to handle metadata for two specific media forms(i.e., QuickTime and MPEG). Objects generated from Track 302 may inheritattributes and methods useful for handling live media, pre-recordedmedia, and/or other media. Among the inherited attributes, for example,may be one that keeps a count of track handles that reference a giventrack.

TrackHandle 304 represents a class of objects configured to facilitatethe streaming of track media to a client using a shared collection oftrack metadata. Illustratively, LiveTrackHandle 340 represents a classof TrackHandle objects configured for streams of live media, whileFileTrackHandle 342 represents a class of TrackHandle objects configuredfor pre-recorded or other stored media. In one alternative embodiment ofthe invention, one type of track handle object (e.g., FileTrackHandle342) may be configured for streaming of both pre-recorded and livemedia. In yet another alternative embodiment, live media may not takethe form of a track and may therefore be served to clients in some othermanner than described herein.

From FileTrackHandle 342, different types of FileTrackHandle objects maybe instantiated for specific forms of media, such as QuickTimeFileTrackHandle 342 a for QuickTime media and MPEG FileTrackHandle 342 bfor MPEG media.

In this embodiment of the invention, each TrackHandle object derivedfrom TrackHandle 304 includes suitable methods for moving to a certaintime index in a media program or track, reading media data into a buffer(for streaming to a client), etc. Thus, TrackHandle objects maintainstate information regarding a client's current play position in a mediatrack, and may include one or more buffers for sending media packets toclients and one or more pointers or references to their correspondingTrack objects for accessing metadata.

Once a FileTrack object is established for a given media track,subsequent client requests for that track use the established FileTrackrather than assembling the track's metadata again. Thus, FileTrackobjects may be configured to instantiate new FileTrackHandle objects fornew client streams.

FIG. 4 demonstrates a method of serving streams of media from one trackto multiple clients while maintaining only one copy of the media'smetadata, according to one embodiment of the invention. In this method,the same media may be streamed to each client, but with differenttiming. That is, different client streams may, at any given time, bestreaming media from different time indices within the media track.

In state 402 of the illustrated procedure, a request is received tostream some pre-recorded media that is not already being streamed. Therequest may, for example, be received as an RTSP command to setup andplay a particular media track. Other forms of requesting media may beused for other protocols or forms of media.

In state 404, the media streaming server creates a Track object tomanage shared access to the requested media's metadata. The illustratedprocedure indicates the creation of a FileTrack object, which asdescribed above, may be configured for pre-recorded media programs andtracks.

In state 406, the FileTrack object extracts and stores the metadata fromthe media track. The FileTrack object may have to parse one or morefiles containing the media track in order to assemble the metadata.

In state 408, a FileTrackHandle is generated for the new client stream,to map or interface between the stream-specific client context and thetrack-specific metadata held by the FileTrack object. TheFileTrackHandle object may be provided with one or more references tothe assembled metadata (e.g., different references for different tablesor different types of metadata). In addition, the FileTrackHandle isallocated a file descriptor or similar resource to facilitate its accessto the file(s) containing the media (e.g., to find and extract media tobe streamed).

In state 410 the requested media is streamed to the new client. Theclient may issue commands to control the stream—e.g., to rewind or fastforward to locate a particular part of the media, to pause thestreaming, etc.

In state 412, while the media is being streamed to one or more clients,the media streaming server is alert for any new requests for the samemedia. If a new request is received, the illustrated procedure returnsto state 408 to set up a new FileTrackHandle object and a new stream.Otherwise, the procedure continues at state 414.

In state 414, the media streaming server determines if all clientstreams of the media have been terminated. The server may make thisdetermination, for example, whenever a client stream is terminated.Illustratively, when a client stream is terminated, its associatedFileTrackHandle object is deleted. If any streams are still in user orestablished, or if any new streams are in the process of being set up,the procedure returns to state 410. Otherwise, the procedure continuesat state 416.

In state 416, after all client streams have ended the FileTrack objectis deleted and the metadata is removed from memory.

One skilled in the art will appreciate that the procedure depicted inFIG. 4 is just one method of sharing a single set of media trackmetadata for multiple client media streams. Other suitable methods maybe derived from the foregoing description without exceeding the scope ofthe invention.

Resynchronizing Media During Streaming

In one embodiment of the invention, a system and methods forresynchronizing a media stream are provided. In this embodiment, a mediastream is considered to be out of synchronization if media for one ormore tracks in the program or event being streamed are not beingstreamed fast enough to keep pace with the time index of the stream. Inother words, a streamed media program's current time index is the timeindex for which all tracks should be sending corresponding media. If themedia for a particular track lags behind the current time index, or nomedia is being streamed at all for the track, then the stream may beconsidered out of synchronization. Loss of synchronization may occur,for example, if a source of a track's media (e.g., a storage device, alive media feed) cannot supply the media at a fast enough rate.

When synchronization is lost, a media streaming server may attempt toresynchronize the media stream by selecting a new, later, media timeindex at which to resume streaming. The server then requests or awaitsmedia corresponding to the new time index and, until the new time indexis reached, the server may cease streaming or may continue streamingmedia that is ready to be transmitted (e.g., for a track that is stillsynchronized).

When the new time index is reached, if the necessary media is receivedthe media streaming server commences streaming the corresponding media.If, however, the media corresponding to the new time index is notavailable when the new time index is reached, the server may makeanother attempt to resynchronize at another, later, new time index andmay allow more time for retrieval of the corresponding media. Attemptsto resynchronize a media stream may be performed a configurable numberof times, and the server may terminate the stream if all attempts areunsuccessful.

FIG. 5 depicts several program objects that may cooperate to facilitateresynchronization of a media stream in one embodiment of the invention.Appropriate corresponding program modules configured to operatesimilarly to the illustrated program objects may be established forcomputer systems using non-object oriented methods of programming.

In FIG. 5, TrackStream 502 represents a class of objects configured toprocess a media track's data for streaming to a client. LiveTrackStream520 represents a TrackStream class of objects configured for streams oflive media, while FileTrackStream 522 represents a TrackStream class ofobjects configured for pre-recorded or other stored media. A TrackStreamobject may include interfaces for retrieving specific track media (e.g.,for a specified time index). From FileTrackStream 522, different typesof FileTrackStream objects may be instantiated or invoked for specificforms of media, such as QuickTime FileTrackStream 522 a for QuickTimemedia and MPEG FileTrackStream 522 b for MPEG media.

In one embodiment of the invention, program objects depicted in FIG. 5may cooperate with objects such as those depicted in and described inconjunction with FIG. 3. In particular, in this embodiment aFileTrackStream object may include or reference a FileTrackHandle objectfor seeking specific locations in a media file, reading data from thefile, etc.

Stream 504 is an abstraction of a media stream to a client. Differenttypes of media streams may be represented by, for example, LiveStream540 for a stream of live media and FileStream 542 for a stream ofpre-recorded media. For different media protocols or forms, differenttypes of stream objects may be created to handle the streaming. Thus, inFIG. 5, FileRTPStream 542 a is configured to stream media to clientsthrough RTP, while FileHTTPStream 542 b is configured to stream mediathrough HTTP.

In the illustrated embodiment of the invention, each Stream objectincludes methods to start, stop, pause and otherwise control a mediastream (e.g., in response to client commands). A Stream object has oneor more sockets with which to communicate with a client, and interactswith, or may even include, a TrackStream object to retrieve media datafor streaming. Illustratively, and because a media stream may comprisemultiple tracks, each Stream object may be associated with, or include,multiple TrackStream objects. For example, if FileRTPStream 542 a iscreated to stream to a client a basic audiovisual media programconsisting of one audio track and one video track, FileRTPStream 542 amay interact with or include separate FileTrackStream objects for eachtrack. As described below, when a track within a media stream gets outof synchronization, the Stream object controlling the streaming mayinitiate a resynchronization procedure.

In one embodiment of the invention, a client connects to a mediastreaming server to request a pre-recorded media program, and a Streamobject of the appropriate type or configuration, such as FileRTPStream542 a is generated to control the streaming of the media. FileRTPStream542 a initiates or invokes one or more TrackStream objects of theappropriate type, such as QuickTime FileTrackStream 522 a. TheFileTrackStream object(s) then create or invoke Track or TrackHandleobjects of the appropriate type or configuration (e.g., as depicted inFIG. 3) to access and retrieve media from the program's track(s). Inthis embodiment, the Stream object controls the streaming (e.g.,starting, stopping, pausing) and resynchronizes the stream if necessary.The TrackStream object(s) control the retrieval of track media byinitiating appropriating tasks and/or invoking interfaces provided bythe Track or TrackHandle objects (e.g., to locate media data, read datafrom a media file).

FIG. 6 demonstrates the resynchronization of a media stream according toone embodiment of the invention. The media to be streamed in theillustrated procedure is pre-recorded and is therefore retrieved fromone or more storage devices, but the procedure may be readily modifiedfor live media received from a live event or other server. In state 602,a pre-recorded media program comprising multiple tracks is beingstreamed to a client by an assigned Stream object (e.g., FileRTPStream542 a of FIG. 5).

In state 604, a request is made or scheduled (e.g., by QuickTimeFileTrackStream 522 a of FIG. 5) to read media data for one of theprogram's tracks from a media file. Illustratively, the requested mediadata corresponds to an upcoming media time index (e.g., movie time).While waiting for the requested data, the Stream object may stream mediadata that is already available (e.g., because it was retrieved earlier),for the same or a different track, or may wait until the requested datashould be available.

In state 606, the Stream object determines whether the requested data isavailable, or may be automatically woken or otherwise alerted when datais received. If the requested data has been received, then the procedurereturns to state 602 to stream the media data at the appropriate mediatime index. In particular, if media data for the program's tracks isreceived in a timely fashion, the Stream object may stream the data atthe corresponding media time index, thereby keeping the media programsynchronized. If the Stream object determines in state 606 that therequested data is not available (e.g., a storage device isover-burdened), thus indicating a loss of synchronization, the procedureadvances to state 608.

In state 608, the Stream object advances or increments the current mediatime index to a future time index and, in state 610, requests media datacorresponding to that future index. Thus, in this embodiment of theinvention, the media streaming server opts to drop or ignore datacorresponding to the media time between the current and future timeindices. Illustratively, any such data (e.g., for a track that has notlost synchronization) may be discarded. The Stream object then goes tosleep or waits an appropriate amount of time for the requested media tobe received.

In state 612, the Stream object determines whether the media datacorresponding to the new media time index has been received and isavailable for streaming. If so, the Stream object returns to state 602to stream the media and retrieve the next portion of media.

However, if the media data is not received and available for streamingat the new time index, in state 614 the Stream object determines whetherit has failed to resynchronize a threshold number of times (e.g.,three). If not, the illustrated procedure returns to state 608 toadvance the media time index once again. Each successive time that thetime index is advanced, it may be advanced by a larger increment. Forexample, if the time index is advanced by a period T the first time, thenext time it may be advanced 2*T, then 4*T, 8*T, etc. Ifresynchronization fails a threshold number of times, the Stream objecthalts the stream and the procedure ends.

One skilled in the art will appreciate that the procedure depicted inFIG. 6 is just one method of resynchronizing a media stream by droppingold media in favor of regaining synchronization at a later time index.Other suitable methods may be derived from the foregoing descriptionwithout exceeding the scope of the invention.

The amount of media data requested or retrieved each time it is neededmay be determined in part by the size or number of available databuffers, the frequency with which data requests are issued, the bit rateat which the media is streamed to a client, etc.

The foregoing descriptions of embodiments of the invention have beenpresented for purposes of illustration and description only. They arenot intended to be exhaustive or to limit the invention to the formsdisclosed. Many modifications and variations will be apparent topractitioners skilled in the art. Accordingly, the above disclosure isnot intended to limit the invention; the scope of the invention isdefined by the appended claims.

1. A method of streaming media to multiple clients, comprising:receiving a request to stream media from a media track to a firstclient; extracting a set of metadata from the media track, wherein saidmetadata facilitates identification and retrieval of the media from themedia track; storing said extracted set of metadata in a memory;streaming the media to the first client in a first stream whilereferring to said stored metadata; and streaming the media to a secondclient in a second stream while referring to said stored metadata. 2.The method of claim 1, further comprising: maintaining a first filedescriptor for retrieving the media from the media track for said firststream; and maintaining a second file descriptor for retrieving themedia from the media track for said second stream.
 3. The method ofclaim 1, wherein the media track is a track of a live media event. 4.The method of claim 1, wherein the media track is a track of apre-recorded media program.
 5. The method of claim 1, furthercomprising: removing said metadata from the memory after said firststream and said second stream are terminated.
 6. A method of using asingle set of media metadata to facilitate streaming the media tomultiple clients, comprising: receiving a request to stream media from afirst media track to a first client, wherein the first media track alsoincludes metadata corresponding to the media; invoking a track moduleconfigured to maintain one copy of said metadata in a memory; operatinga first track handler to stream the media to the first client, whereinsaid first track handler accesses said metadata to facilitate saidstreaming; receiving a request to stream the media to a second clientbefore said streaming of the media to the first client is terminated;and operating a second track handler to stream the media to the secondclient, wherein said second track handler accesses said metadata tofacilitate said streaming; wherein said metadata is configured tofacilitate retrieval of the media from the first media track.
 7. Themethod of claim 6, wherein said operating a first track handlercomprises using a first file descriptor to retrieve the media from thefirst file track; and said operating a second track handler comprisesusing a second file descriptor to retrieve the media from the first filetrack.
 8. The method of claim 6, wherein said operating a first trackhandler comprises: establishing a first set of references to saidmetadata; using said first set of references to identify a first portionof the media to be streamed to the first client for a first time index;and using said first set of references to locate said first mediaportion in the first media track.
 9. The method of claim 8, wherein saidoperating a second track handler comprises: establishing a second set ofreferences to said metadata; using said second set of references toidentify a second media portion to be streamed to the second client fora second time index; and using said second set of references to locatesaid second media portion in the first media track.
 10. The method ofclaim 9, wherein said first set of references and said second set ofreferences are used to access said metadata simultaneously.
 11. Acomputer readable storage medium storing instructions that, whenexecuted by a computer, cause the computer to perform a method ofstreaming media to multiple clients, the method comprising: receiving arequest to stream media from a media track to a first client; extractinga set of metadata from the media track, wherein said metadatafacilitates identification and retrieval of the media from the mediatrack; storing said extracted set of metadata in a memory; streaming themedia to the first client in a first stream while referring to saidstored metadata; and streaming the media to a second client in a secondstream while referring to said stored metadata.
 12. A computer readablestorage medium containing a data structure configured for facilitatingthe simultaneous streaming of media from a media track to multipleclients, the data structure comprising: a set of metadata configured toassociate time indices of the media track with corresponding portions ofthe media, and to locate said corresponding portions within the mediatrack; wherein said set of metadata is simultaneous accessed by each ofmultiple client stream handlers, wherein each stream handler isassociated with a different client, to facilitate retrieval of differentportions of the media for streaming to their respective clients.
 13. Anapparatus for streaming media to clients, comprising: a first track of amedia program stored on a first storage device, the first media trackcomprising: media; and metadata configured to facilitate access to themedia; a first memory; a set of track handle modules, wherein each ofsaid track handle modules is configured to facilitate streaming themedia to a different client; and a track module configured to store saidmetadata in said first memory for shared access by said track handlemodules; wherein said track handle modules access said metadata toidentify portions of the media and locate said portions on the firststorage device.
 14. The apparatus of claim 13, wherein each of saidtrack handle modules is allocated a separate file descriptor forretrieving the media from the first storage device.
 15. The apparatus ofclaim 13, wherein each of said track handle modules simultaneouslyaccesses said metadata in said first memory.
 16. The apparatus of claim15, wherein said simultaneous accesses to said metadata are configuredto identify different portions of the media.
 17. The apparatus of claim13, wherein said media portions are associated with time indices withinsaid first media track and said metadata is configured to identify, fora given time index, said associated media portion.
 18. The apparatus ofclaim 17, wherein said metadata is further configured to identify, for agiven media portion, a location on said first storage device at whichsaid given media portion is stored.